PROJECT SUMMARY Glioblastoma multiforme (GBM) is the most common and aggressive primary human brain tumor and is invariably fatal. Standard of care includes debulking of tumor, normally through surgery; however, not all GBM tumors or patients are eligible for the procedure. Ablation is an effective alternative to surgical resection, and can be performed noninvasively with transcranial focused ultrasound. In the proposed project, transcranial focused ultrasound will be combined with a novel phase-shift nanoemulsion (PSNE) for focal nonthermal ablation of GBM tumors. PSNE can be vaporized with ultrasound pulses and the resultant bubbles can generate intense mechanical forces that can collapse blood vessels or fractionate tissue. Vaporization of the nanoemulsions selectively in established GBM tumors will enable highly localized nonthermal ablation of intracranial tumors while sparing surrounding healthy brain tissue. To test this premise, we will evaluate the extent of damage and immune response to ablation (i.e. immune cell infiltration) within and adjacent to sonicated brain tumors as a function of acoustic pressure and PSNE concentration. We will also analyze ablated regions for expression of ceramide, an apoptotic promoter that reportedly enhances the efficacy of radiotherapy by more than 10-fold. Lastly, we will assess the impact of nonthermal focal ablation on the survival of tumor-burdened rats. Overall, we aim to elucidate the parameters that facilitate safe and effective ultrasound-mediated nonthermal ablation of primary brain tumors.